IL-13 is a short-chain cytokine sharing 25% sequence identity with IL-4. It comprises approximately 132 amino acids, forming a secondary structure of four helices spanning residues 10-21 (helix A), 43-52 (helix B), 61-69 (helix C), and 92-110 (helix D), along with two β-strands spanning residues 33-36 and 87-90. The solution structure of IL-13 has been solved, revealing the predicted up-up-down-down four-helix-bundle conformation also observed with IL-4 (Eisenmesser 2001).
Human IL-13 is a 17-kDa glycoprotein cloned from activated T cells (Zurawski and de Vries 1994 Immunol Today 15 19-26), and is produced by activated T cells of the Th2 lineage, although Th0 and Th1 CD4+ T cells, CD8+ T cells, and several non-T cell populations such as mast cells also produce IL-13 (Zurawski and de Vries 1994 Immunol Today 13 19-26).
The function of IL-13 includes:                immunoglobulin isotype switching to IgE in human B cells (Punnonen, Aversa et al. 1993 Proc Natl Acad Sci USA 90 3730-4) and        suppressing inflammatory cytokine production in both humans and mice (de Waal Malefyt, Figdor et al. 1993 J Immunol 151 6370-81; Doherty, Kastelein et al. 1993 J Immunol 151 7151-60).        
IL-13 binds to its cell surface receptors, IL-13 Ralpha1 and IL-13 Ralpha2. IL-13Ralpha1 interacts with IL-13 with a low affinity (KD −10 nM), followed by recruitment of IL-4Ra to form the high affinity (KD ˜0.4 nM) signaling heterodimeric receptor complex (Aman, Tayebi et al. 1996 J Biol Chem 271 29265-70; Hilton, Zhang et al. 1996 Proc Natl Acad Sci USA 93 497-501).
The IL-4R/IL-13Ralpha1 complex is expressed on many cell types such as B cells, monocyte/macrophages, dendritic cells, eosinophils, basophils, fibroblasts, endothelial cells, airway epithelial cells, and airway smooth muscle cells (Graber, Gretener et al. 1998 Eur J Immunol 28 4286-98; Murata, Husain et al. 1998 Int Immunol 10 1103-10; Akaiwa, Yu et al. 2001 Cytokine 13 75-84).
Ligation of the IL-13Ralpha1/IL-4R receptor complex results in activation of a variety of signal-transduction pathways including signal transducer and activator of transcription (ST AT6) and the insulin receptor substrate-2 (IRS-2) pathways (Wang, Michieli et al. 1995 Blood 864218-27; Takeda, Kamanaka et al. 1996 J Immunol 157 3220-2).
The IL-13Ralpha2 chain alone has a high affinity (KD ˜0.25-0.4 nM) for IL-13, and functions as both a decoy receptor negatively regulating IL-13 binding (Donaldson, Whitters et al. 1998 J Immunol 161 2317-24), and a signaling receptor that induces TGF-b synthesis and fibrosis via AP-I pathway in macrophages and possibly other cell types (Fichtner-Feigl, Strober et al. 2006 Nat Med 12 99-106).
Several studies conducted in preclinical animal models for asthma indicate that IL-13 plays an important role in asthma. These data include resistance to asthma in the IL-13 knockout mice as well as inhibition of the asthma phenotype with IL-13 antagonists (soluble IL-13 receptors, anti-IL-13 mAbs, etc.) in various mouse models (Sela 1999 Harefuah 137 317-9; Wills-Karp and Chiaramonte 2003 Curr Opin PuIm Med 9 21-7; Wills-Karp 2004 Immunol Rev 202 175-90). Multiple studies have demonstrated that pharmacologic administration of recombinant IL-13 to the lungs of mice as well as guinea pigs induces airway mucus hyper-secretion, eosinophilia and AHR (Grunig, Warnock et al. 1998 Science 282 2261-3; Wills-Karp, Luyimbazi et al. 1998 Science 282 2258-61; Kibe, Inoue et al. 2003 Am J Respir Crit Care Med 167 50-6; Vargaftig and Singer 2003 Am J Physiol Lung Cell MoI Physiol 284 L260-9; Vargaftig and Singer 2003 Am J Respir Cell MoI Biol 28 410-9).
These effects of IL-13 are reproduced in transgenic mouse systems with either constitutive or inducible expression of IL-13 (Zhu, Homer et al. 1999 J Clin Invest 103 779-88; Zhu, Lee et al. 2001 Am J Respir Crit Care Med 164 S67-70; Lanone, Zheng et al. 2002 J Clin Invest 110463-74). Chronic transgenic over-expression of IL-13 also induces subepithelial fibrosis and emphysema. Mice deficient in the IL-13 (and IL-4) signaling molecule STAT6 fail to develop allergen-induced AHR and mucus overproduction (Kuperman, Huang et al. 2002 Nat Med 8 885-9). Studies using soluble IL-13 receptor fusion protein (sDL-13Ralpha2Fc) have demonstrated the pivotal role of this cytokine in experimental allergen ovalbumin (OVA)-induced airway disease (Grunig, Warnock et al. 1998 Science 282 2261-3; Wills-Karp, Luyimbazi et al. 1998 Science 282 2258-61; Taube, Duez et al. 2002 J Immunol 169 6482-9).
Efficacy of anti-IL-13 treatment was also demonstrated in a chronic model of murine asthma. In addition to exhibiting features of mucus hyper-secretion and AHR, this model of chronic asthma demonstrates several hallmarks of human disease that are lacking in the more acute models. These include eosinophilia of the lung tissue located in inter-epithelial spaces as well as smooth muscle fibrosis as measured by increases in collagen deposition. The chronic asthma model is induced with repeated aerosol challenges with OVA in OVA-sensitized mice 1×/week for a total of 4 weeks. Anti-IL-13 antibody administered for the final 2 weeks of OVA challenges (from day 36 with efficacy readouts assessed on day 53 of study) significantly inhibited AHR, pulmonary inflammation, goblet cell hyperplasia, mucus hypersecretion, and airway fibrosis (Yang, Li et al. 2005 J Pharmacol Exp Ther).
The therapeutic effect of IL-13 antagonist was also demonstrated to inhibit AHR in a primate model of asthma, (American Thoracic Society, San Diego 2005).
IL-13 is implicated in the pathogenesis of human asthma as elevated levels of IL-13 mRNA and protein have been detected in lungs of asthmatic patients, which correlate with severity of the disease (Huang, Xiao et al. 1995 J Immunol 155 2688-94). In addition, human IL-13 genetic polymorphisms, which lead to elevated IL-13 levels, have been identified and are associated with asthma and atopy (Heinzmann, Mao et al. 2000 Hum MoI Genet 9 549-59; Hoerauf, Kruse et al. 2002 Microbes Infect 4 37-42; Vercelli 2002 Curr Opin Allergy Clin Immunol 2 389-93; Heinzmann, Jerkic et al. 2003 J Allergy Clin Immunol 112 735-9; Chen, Ericksen et al. 2004 J Allergy Clin Immunol 114 553-60; Vladich, Brazille et al. 2005 J Clin Invest), and elevated IL-13 levels have been detected in the lung of asthma patients (Huang, Xiao et al. 1995 J Immunol 155 2688-94; Arima, Umeshita-Suyama et al. 2002 J Allergy Clin Immunol 109 980-7; Berry, Parker et al. 2004 J Allergy Clin Immunol 114 1106-9). A genetic linkage between IL-13 and asthma has also been demonstrated as individuals with a polymorphism in the IL-13 gene which causes higher plasma IL-13 levels have an increased risk for atropy and asthma (Wills-Karp 2000 Respir Res 1 19-23).
Due to the role of human IL-13 in a variety of human disorders, therapeutic strategies have been designed to inhibit or counteract IL-13 activity. In particular, antibodies that bind to, and neutralize, IL-13 have been sought as a means to inhibit IL-13 activity. However, there exists a need in the art for suitable and/or improved antibodies capable of binding IL-13, especially human IL-13. In particular the antibodies are capable of neutralizing human IL-13. The present invention provides a novel family of binding proteins, CDR grafted antibodies, humanized antibodies, and fragments thereof, capable of binding human IL-13, binding with high affinity, and binding and neutralizing human IL-13.